This invention relates to fuel injection devices for spark ignition type internal combustion engines, and more particularly to control devices for controlling the amount of fuel that is to be injected into the air inlet passage to the cylinders of internal combustion engines.
Conventionally, the supply of fuel to the spark ignition type internal combustion engines of passenger automobiles has been effected by carburetors; recently, however, fuel injectors are becoming increasingly common. These fuel injectors are capable of supplying a precisely controlled amount of fuel to the internal combustion engine so as to obtain an optimum air-fuel ratio. In the case of the conventional fuel injectors, the amount of fuel injected into the air inlet passage to the cylinders of an engine is determined as follows:
The air pressure within the air intake passage to the engine is detected by an air pressure sensor, and converted into an air pressure data; then, the variation of the air pressure data is compared with a predetermined threshold level to determine whether the engine is in the transient state or not; further, in accordance with the result of this determination, the amount of fuel to be injected is calculated on the basis of the above pressure data. An amount of fuel corresponding to this calculated amount is injected in synchrony with a predetermined crank angle of the engine.
The conventional fuel injectors therefore has the following disadvantages: When the load of the engine is high, the ripples contained in the pressure data (i.e., the small fluctuations resulting from pulsations of the air current in the air inlet passage to the engine) become consipicuous. Thus, erroneous detections of a transient state of the engine tend to occur due to these ripples; if this is to be avoided, the threshold level with which the variation of the pressure data is compared must be set at a relatively high value. The high threshold value, however, results in the lower sensitivity of transience detection; thus, the detection of transience of the engine is retarded when the engine is under the low load condition, and, consequently, the adaptation of the injected amount of fuel to the rapidly changing condition of the engine is belated. As a result, the air-fuel ratio is deviated from the optimum level, and the performance of the engine is impaired.
If, on the other hand, the threshold level with which the variation of the pressure data is compared is set at a relatively low value, the sensitivity of transience detection is improved; however, erroneous detections of transience tend to occur, which result in an abonormally rich air-fuel mixture. Consequently, the driving performance is impaired and the cost of fuel is increased.